In the field of mobile communication systems, including cellular communication systems, terminal speed is a relevant parameter in various contexts and for various purposes. This is due to the fact that terminal mobility represents a paramount aspect in mobile (cellular) communication systems, and various procedures and/or parameters depend on terminal mobility characteristics, including terminal speed.
For example, an appropriate setting of handover (HO) parameters depends, among others, on the speed of a terminal (or UE) in question. Relevant HO parameters may for example include time-to-triggers and signal strength thresholds, which usually depend heavily on terminal speed. In general, pedestrian terminals require longer HO parameters compared with fast moving terminals. If handover parameters are set to favor fast moving terminals, then pedestrian terminals face (many) unnecessary ping-pong handovers. In contrast, if handover parameters are set to favor pedestrian terminals, then fast moving terminals face (many) unnecessary radio link failures. In view thereof, in order to improve network performance by minimizing handover-related radio link failures and ping-pong handovers, it is desirable to set handover parameters in accordance with terminal speed (and other relevant requirements and/or constraints).
Since the terminal speed varies from UE to UE and there are usually many UEs connected to a serving base station simultaneously, this means that a static or a dynamic setting of HO parameters cannot be done globally in a cell for the all UEs in an appropriate manner. This is because in that case only some of the UEs would benefit from the setting and at the same time some of the UEs would suffer therefrom.
If the speed or a mobility state of a terminal (or UE) could be detected reliably enough, then HO parameter setting could be done in a UE-specific manner. This would mean that HO parameters of a single UE could be tuned according to the UE speed or mobility state to avoid mobility-related HO problems.
However, mobile communication systems do typically not include specific facilities for reliably detecting terminal speed. Therefore, especially for terminals which do not include dedicated auxiliary facilities such as a navigation system (e.g. a GNSS on the basis of GPS), it is problematic to reliably detect terminal speed, especially in terms of requirements and/or constraints regarding accuracy, duration (delay) and/or demand for dedicated hardware/software.
There exist some solutions for terminal speed estimation in mobile communication systems. Such proposals include, for example, assignment (classification) of a UE mobility state between low, medium and high velocity UEs based on the UE handover and/or cell re-selection rate. However, such approach suffers from being too slow and from being not accurate enough or unreliable, especially in heterogeneous network environments where cell sizes vary, thus affecting the handover and re-selection rate and mobility classification as well. Such proposals also include, for example, estimation of UE speed from LTE downlink reference signals, rate of timing advancing and magnitude of timing-offset. Further proposals include, for example, improvements to existing specifications and other measurements such as Doppler spread estimation and other measurements related to the Doppler spread e.g., level-crossing-rate and an average-fade-duration measurements. Such proposals suffer from being too slow and/or from requiring dedicated hardware/software for performing corresponding measurements and/or signal processing.
In view thereof, there exist problems in reliably detecting terminal speed in mobile communication systems, especially in terms of requirements and/or constraints regarding accuracy, duration (delay) and/or demand for dedicated hardware/software.
Thus, there is a need to further improve terminal mobility state detection.